Human culture and departure from Africa may be unrelated to population levels.

About 50,000 years ago, modern humans left Africa and began occupying the rest of the world. The common thought is that a sudden growth in population caused the so-called “human revolution,” which gave birth to language, art, and culture as we know it today. Now, based on something that’s not obviously related to human culture—the size of shellfish fossils—researchers have challenged that model.

Artifacts from two sites in South Africa, Still Bay and Howieson’s Poort, have convinced archaeologists that the period between 85,000 to 65,000 years ago was when the “human revolution” began. Humans from that time made jewelry from perforated shells and used objects as symbols. They made better tools than they had ever before. Some of these tools, made from ostrich eggshells, were even capable of slicing fruit.

It has been thought that this period also saw a sudden explosion in population growth. Now, Richard Klein from Stanford University and Teresa Steele from the University of California at Davis argue that archaeologists and anthropologists have got it wrong. In a study published in the Proceedings of the National Academy of Sciences, they say there is evidence to suggest that population did not actually explode during this period.

Klein and Steele’s evidence comes from the size of shellfish fossils from that period. Higher predation of shellfish forces their shells to become smaller, and there is no evidence of shellfish shrinkage during this time.

According to Robert Foley, an expert on the origins of modern humans at Cambridge University, the idea is not as far-fetched as it sounds. “Other things remaining equal, there is a strong relationship between shell size and human predation,” he said. This correlation can be seen in shellfish around the world today. Coasts where shellfish are collected en masse see animals with smaller shells than those where shellfish aren’t collected.

The evidence for Klein and Steele’s claim comes from the South Africa, which seems to be the only place that has well-preserved shellfish fossils from that period. They find that the shell size during the Middle Stone Age (MSA, about 200,000 years ago) and Later Stone Age (LSA, about 50,000 years ago) were not much different. Thus, they say, this period must not have seen a sudden population explosion, as many argue.

But Martin Zeigler, climate geologist at the Swiss Federal Institute of Technology in Zurich, is not entirely convinced. “Environmental factors could affect shellfish size on the timescales that are studied here,” he said. And he is right. Many factors are involved in determining shell size, such as water temperature, salinity, nutrient availability, and species population.

Klein and Steele argue that we will never have enough information on how much these factors played a role. But with studies on contemporary shellfish showing the same trend, it's hard to argue against the hypothesis without some evidence showing that it’s wrong.

Foley has respect for Klein’s work. He said, “They do tackle limitations in their study by pointing out that rising sea-level has removed the relevant sites from the recent LSA period of about 10,000 years ago. While one has to be cautious about the overall implications of their analysis for the evolution of modern humans, it is not very likely that rising population could ever be a complete explanation.”

Klein and Steele believe that the innovations that happened in Still Bay and Howieson’s Poort at the time cannot be explained by an enhancement in human ability to survive and reproduce. Instead, they argue that other reasons, such as climate fluctuations and genetic changes, may explain what caused the human revolution.

I don't get the nuance here. What's the deal with the 50,000 BCE date and how that marks "modern" humans? Based on what evidence?

that's roughly the time we started migrating out of Africa, started using tools, started developing agriculture, making settlements, etc. that's why it's seen as the start of "modern" human civilization, as opposed to nomadic hunter/gatherer lifestyle

I never understood this. By "leave Africa" do they mean no one stayed behind? Was Africa later repopulated? If people stayed behind what percentage left? I'd really like to know about human life in Africa circa 20,000 BCE during the last glaciation period. Unfortunately everything I find for that time period is about Europe.

I don't get the nuance here. What's the deal with the 50,000 BCE date and how that marks "modern" humans? Based on what evidence?

that's roughly the time we started migrating out of Africa, started using tools, started developing agriculture, making settlements, etc. that's why it's seen as the start of "modern" human civilization, as opposed to nomadic hunter/gatherer lifestyle

What? It's about the time we were migrating out of a Africa. Manufactured stone tools have been used since before our species was even on the horizon. Actual agriculture wasn't around until less than 20,000 years ago, and didn't really take hold until the end of the Younger Dryas event. Similarly, there's not a lot of evidence for permanent human settlements until 25K years ago.

I never understood this. By "leave Africa" do they mean no one stayed behind? Was Africa later repopulated? If people stayed behind what percentage left? I'd really like to know about human life in Africa circa 20,000 BCE during the last glaciation period. Unfortunately everything I find for that time period is about Europe.

By "leave" Africa they mean the same thing as children "leaving" their parents' house to live on their own. Africa has always been population as long as there were humans, but it wasn't until about this time that modern humans started spreading out in into the rest of the world too.

Maybe they didn't prey on shellfish because they were allergic, didn't like them, or had a religion that worshiped them. I don't prey on the ants that live outside my house but that doesn't mean I don't exist.

Hmmm....seems odd to think we had a population explosion. What exactly does that mean? The nomadic tribes still needed to range and get food. Move from one place eat everything around, move over a bit more and eat everything editable. We got more useful calories from having things cooked, cooking makes digestion less energy intensive. There became a bit more densely population. Increase spreading makes sense. Explosion expresses density, this I would disagree.

The people would still have the same technology to gain shellfish. More people does not equal better at it, they ate whatever they could reasonably get.

I think the biggest thing was the social change. Why did we become so social, how was this trait was rapidly evolved. IMO natural evolution doesn't account for it. My thoughts are of infanticide. Killing excess babies had a way of managing populations and a very high level of evolutionary pressure to socialness. Who's babies were kept.

I think the biggest thing was the social change. Why did we become so social, how was this trait was rapidly evolved. IMO natural evolution doesn't account for it. My thoughts are of infanticide. Killing excess babies had a way of managing populations and a very high level of evolutionary pressure to socialness. Who's babies were kept.

What do you mean by "so social?" All our identifiably proto-human ancestors were social, just like chimps and gorillas are today.

I would have thought the population growth would have also tied to expansion, more humans over a larger area wouldn't put as much stress on the shellfish population in the sense of today's humans putting stress on a population (they didn't fish heavy in a location then export the shellfish, they would have eaten what was nearby). We spread out over the entire world fairly quickly due to the ice age receding, it wouldn't make sense to heavily attack one population of fish (also, South Africa wasn't exactly the birthplace of humanity either, it was further north).

I also thought the real explosion started with agriculture a few tens of thousands of years later.

I never understood this. By "leave Africa" do they mean no one stayed behind? Was Africa later repopulated? If people stayed behind what percentage left? I'd really like to know about human life in Africa circa 20,000 BCE during the last glaciation period. Unfortunately everything I find for that time period is about Europe.

There are believed to have been many waves of migration of out africa, at least 4. It doesn't mean all people left, just possibly "tribes". A wave went to oceania/south asia -they are related to modern australia natives, not asians-, a different wave went to Siberia and eastern europe -presumed extinct afaik-, at least a couple of waves colonized europe and asia at different times, encroaching into what was Neanderthal territory. Also, the effect of the last glaciation in africa was in the form of "drying out", the Sahara desert grew dramatically, the savanna developed into what we know today (arid grasslands), and the tropical forest where relegated to southern end of the continent.

I never understood this. By "leave Africa" do they mean no one stayed behind? Was Africa later repopulated? If people stayed behind what percentage left? I'd really like to know about human life in Africa circa 20,000 BCE during the last glaciation period. Unfortunately everything I find for that time period is about Europe.

There are believed to have been many waves of migration of out africa, at least 4. It doesn't mean all people left, just possibly "tribes". A wave went to oceania/south asia -they are related to modern australia natives, not asians-, a different wave went to Siberia and eastern europe -presumed extinct afaik-, at least a couple of waves colonized europe and asia at different times, encroaching into what was Neanderthal territory. Also, the effect of the last glaciation in africa was in the form of "drying out", the Sahara desert grew dramatically, the savanna developed into what we know today (arid grasslands), and the tropical forest where relegated to southern end of the continent.

i don't think so - only one wave successfully made it out of africa, expanding along the coastlines around asia and subsequently up rivers. when the sea level was low they crossed into the americas and australia, which were cut off when sea levels rose again. the americas have had three waves of migration from asia.

after the ice age, humans expanded into europe mixing with neanderthals (europeans have about 4% neanderthal dna).

the african tropical forests tend to be in the center of the continent, btw - not the southern end.

I think the biggest thing was the social change. Why did we become so social, how was this trait was rapidly evolved. IMO natural evolution doesn't account for it. My thoughts are of infanticide. Killing excess babies had a way of managing populations and a very high level of evolutionary pressure to socialness. Who's babies were kept.

I can't see the presence of infanticide in times of hardship being a novel development, or one with a sweeping evolutionary pressure in the relatively egalitarian hunter-gatherer societies of large mobile kinship groups which almost certainly would have been the norm for our ancestors at that time. Only after population densities increased with the birth of cities during the last 10,000 years, and after social stratification became the norm, would such pressures be significant. Indeed, a case of the significance of "whose babies survived" in a more developed society was seen in the Middle Ages--mortality among the lower strata was significantly greater than in the upper (particularly when the Plagues killed 2/3 of Europe), leading to downward mobility for the extra children of the wealthy who couldn't sustain themselves in an age of incipient primogeniture (thus spreading a more educated culture downward) and an upward mobility for those in the masses with ability. Arguably in large part because of this, a thriving and volatile middle class became established, and this laid the foundations for very significant cultural evolution.

I see the so-called "human revolution" as something of a mirage. We're looking for what we want to see and convincing ourselves we see it, when it fact it just doesn't exist. We want to see one easy, obvious answer, a simple development we can point to and say "that's what made us behaviorally modern humans, and here's why it did that." I think the reality of the matter is that our behavioral evolution was shaped by the same small, cumulative forces which shape all evolution. Nothing big or physically obvious made us behaviorally modern; I think the evidence points to the conclusion that we've had the "hardware" which makes us capable of modernity for at least twice as long as we've had the "software"--and that we've probably had most or perhaps all of it for hundreds of thousands of years.

For example, there was much speculation prior to the sequencing of the Neandertal genome that they'd have a different version of the FOXP2 gene, and that this would somehow explain our modernity as a function of development of language hardware; but not only did Neandertals share the same FOXP2 as us--it turns out even Denisovans did. Geneticists had projected that, based purely on expected rates of molecular evolution, FOXP2 should have developed much closer to the present; but the reality is that human population histories have been extremely complex--increasingly so as we approach the present--and it's unreasonable to use simple models to assume too much.

Humans have been doing complex and surprising things for far longer than our assumptions and preconceptions about modernity would suggest. As I mentioned in another recent comment, even our very recent history has been filled with peaks and valleys of cultural complexity which have been almost cyclical. The evidence of the closeness of Neandertal and Denisovan genomes to our own--and the fact that some Melanesians and other contemporary peoples probably average up to 10% "archaic" Denisovan and Neandertal inheritance--should give us pause to consider how much of what we are is due entirely to cultural "software" and not biological "hardware." There was perhaps no "human revolution" at all, just tens of generations of culture developing along the right lines (without getting wiped out as it had many times before) to give us software finally capable of exploiting the hardware capabilities which had always or mostly been there for around a quarter-million years or more. The human "last mile" is almost all culture, not genes.

Now, this isn't to say that we haven't undergone profound genetic evolution since then--we have, because our population has exploded at least twice recently and our evolution has accelerated. I'm just pointing out that the fundamental hardware foundations for those things which make us human, like the speech capabilities reflected by our FOXP2 alleles, are probably very ancient. The cultural software to use them fully, however, is probably fairly new--and it's the development of that software which we're mistakenly trying to attribute to some physical cause when it's just the result of generations of cumulative cultural inheritance finally stumbling "in the right direction." The genetic evolution we've experienced since then has been very significant, and has in fact accelerated--but mostly in terms of things like lactase persistence, which aren't exactly fundamental to whatever it means to be human.

Human culture and departure from Africa may be unrelated to population levels.

Of course, is there any controversy or serious debate about that?

Even neanderthals and other subspecies migrated from Africa before homo sapiens sapiens did it , so i do not know how to correlate "human" culture with leaving Africa and population levels . How you figure that assumption?

BTW, i think that modern europeans are the product of neanderthals , homo sapiens and other subspecies , this is just a random baseless, ignorant and speculative thought

I thought it was octopi? I guess it's kind of like the plural of fish was fish, now it's fishes in that the plural changed.

Anyways my thought on this is why would human population necessarily stick to the shore lines instead of moving further inland on different land masses?

I'm just making an assumption here that maybe there were more desirable resources found further from shore. This isn't something I know enough to really say for sure. I do know beach front property is desirable but not everyone enjoys the beach.

The problem is that, at best, this only shows that humans weren't living more densely around acquatic environments. It doesn't show total population wasn't growing and doesn't show that there wasn't growing density in other environments.

It does, potentially, put some bounds on what might have been happening to some human populations, so is still useful research. But I think the overarching conclusion is overstated.

I thought it was octopi? Kind of like the plural of fish was fish, now it's fishes.

Octopus is greek, not latin, so should never have been fitted with a latin plural form. Octopodes is the plural in greek. However, there's an even stronger argument that just because we borrow a word from a foreign language, doesn't mean we need to apply the foreign plural form to that word. "Octopus" is just as much an english words as thousands of other borrowed words. Why don't we just use the english plural?

EDIT: But I'll bet a lexicographer would say that both "octopuses" and "octopi" are common enough in usage to be accepted as english words, but that "octopodes" is only seen rarely, so maybe we should just let that one die.

Maybe they didn't prey on shellfish because they were allergic, didn't like them, or had a religion that worshiped them. I don't prey on the ants that live outside my house but that doesn't mean I don't exist.

The chances of seeing an entire population that is allergic are so vanishingly small as to be considered beyond unlikely. While it's dangerous to assume, of course, and I applaud the question, there is good evidence that humans of this time period and before were, in fact, preying on shellfish. Dr Curtis Marean has previously published research showing humans were doing so much earlier, ~160K YA, as I recall, though I'm too lazy to dig out the actual cites ... I'm sure they're in the link to him , if you want to dig them up. There's simply no reason to assume humans would stop eating something en masse once they start. There are other papers documenting shellfish use but I don't have any quite on the top of my head. Dr Marean's is one I read fairly recently. It's interesting because his site coincides with a timeframe when we're pretty sure there were only 1000 humans left alive and it's possible that shellfish predation saved their asses when other, historical, food sources had dried up ... almost literally so.

Maybe they didn't prey on shellfish because they were allergic, didn't like them, or had a religion that worshiped them. I don't prey on the ants that live outside my house but that doesn't mean I don't exist.

YOu wouldn't have an entire population that is allergic. While it's dangerous to assume, of course, one would think that they probably have evidence that humans of this time period were, in fact, preying on shellfish. Dr Curtis Marean has previously published research showing humans were doing so much earlier, ~160K YA, as I recall, though I'm too lazy to dig out the actual cites ... I'm sure they're in the link to him , if you want to dig them up. There's simply no reason to assume humans would stop eating something en masse once they start.

There's plenty of evidence that shellfish was a signficant portion of the human diet (where available).

I thought it was octopi? Kind of like the plural of fish was fish, now it's fishes.

Octopus is greek, not latin, so should never have been fitted with a latin plural form. Octopodes is the plural in greek. However, there's an even stronger argument that just because we borrow a word from a foreign language, doesn't mean we need to apply the foreign plural form to that word. "Octopus" is just as much an english words as thousands of other borrowed words. Why don't we just use the english plural?

EDIT: But I'll bet a lexicographer would say that both "octopuses" and "octopi" are common enough in usage to be accepted as english words, but that "octopodes" is only seen rarely, so maybe we should just let that one die.

Random House says octopuses and octopi are both valid. Collins says only octopuses. I'm sure you can find other dictionaries that support both views.

I've never heard "octopodes" in actual use. It may be etymologically more valid, but if English cared about that, well, it wouldn't be English.

Really, I thought I was getting away with something by using "mglw'nafh" and not "mglw'nafhs". The conjugation is all wrong due to the English source not really knowing the original language.

Klein and Steele’s evidence comes from the size of shellfish fossils from that period. Higher predation of shellfish forces their shells to become smaller, and there is no evidence of shellfish shrinkage during this time.

This may well be true at todays rate of consumption, but I cannot imagine that the population 50k years ago was so large and efficient at gathering shellfish as to make any difference. To put it another way, there is probably a lower bounds below which this effect is not seen.

There seem to be a confusion here between population growth and population density.If the population density rises in an area of a preditory species then yes there will be obvisious signs in the condition of the prey species in that area ... But if the population rises but is not followed by an increase in population density, because the population expands into other areas as extra sons and daughters are sent off rather than stay, then there is no significant change in the prediation rates of the prey animals in that particular area, they don't care about what happening inthe next bay over, .. As a species they mght be effected but for the ones in that particular bay things are just like before.

Klein and Steele’s evidence comes from the size of shellfish fossils from that period. Higher predation of shellfish forces their shells to become smaller, and there is no evidence of shellfish shrinkage during this time.

This may well be true at todays rate of consumption, but I cannot imagine that the population 50k years ago was so large and efficient at gathering shellfish as to make any difference. To put it another way, there is probably a lower bounds below which this effect is not seen.

Yeah, I'm having trouble with this assertion too. It's pretty hard to believe that the human population at the time would exert evolutionary pressure on clams, including human predation on clam or shellfish predators.

Also this assertion:

"Artifacts from two sites in South Africa, Still Bay and Howieson’s Poort, have convinced archaeologists that the period between 85,000 to 65,000 years ago was when the “human revolution” began."

The "constant" shellfish size claim counters this claim. But what, what, what? We have one assertion, based on sites in South Africa, the southern tip of the African continent? Kind of a dubious linkage there without further evidence or finds. Then there is a counter-claim, based on the size of shellfish?

Maybe they didn't prey on shellfish because they were allergic, didn't like them, or had a religion that worshiped them. I don't prey on the ants that live outside my house but that doesn't mean I don't exist.

YOu wouldn't have an entire population that is allergic. While it's dangerous to assume, of course, one would think that they probably have evidence that humans of this time period were, in fact, preying on shellfish. Dr Curtis Marean has previously published research showing humans were doing so much earlier, ~160K YA, as I recall, though I'm too lazy to dig out the actual cites ... I'm sure they're in the link to him , if you want to dig them up. There's simply no reason to assume humans would stop eating something en masse once they start.

There's plenty of evidence that shellfish was a signficant portion of the human diet (where available).

Exactly. I clarified somewhat. I posted the first version via my phone, which I should know better than to do.

Klein and Steele’s evidence comes from the size of shellfish fossils from that period. Higher predation of shellfish forces their shells to become smaller, and there is no evidence of shellfish shrinkage during this time.

This may well be true at todays rate of consumption, but I cannot imagine that the population 50k years ago was so large and efficient at gathering shellfish as to make any difference. To put it another way, there is probably a lower bounds below which this effect is not seen.

And what makes you think they don't know this lower bound? I don't have it on hand but it's very well documented in general. As I recall, it's pretty darned low, too. Since shellfish are a very good food source for such a society. Heck, they're pretty good for us now but back then, they had a great mix of nutrients and while the ancient peoples probably didn't know precisely why, it's almost certain that their bodies would have started craving the shellfish once exposed to it.

On a side note, I hate seafood despite growing up in a fishing village. I've long recognized that should the world fall apart (and I survive, of course) I'm going to have to learn to deal with it.

Yeah, I'm having trouble with this assertion too. It's pretty hard to believe that the human population at the time would exert evolutionary pressure on clams, including human predation on clam or shellfish predators.

It's not evolutionary, it's biological. As shellfish grow, their shells get bigger. When humans prey upon them, we take the biggest (oldest) ones. This leaves fewer of the big ones to become fossils.

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Also this assertion:

"Artifacts from two sites in South Africa, Still Bay and Howieson’s Poort, have convinced archaeologists that the period between 85,000 to 65,000 years ago was when the “human revolution” began."

The "constant" shellfish size claim counters this claim. But what, what, what? We have one assertion, based on sites in South Africa, the southern tip of the African continent? Kind of a dubious linkage there without further evidence or finds. Then there is a counter-claim, based on the size of shellfish?

The two aren't at odds. The two sites claimed to show the start of the "revolution" are dealing with when we, as a species, began to develop certain cultural aspects. This happens to coincide with the diaspora out of Africa (or one of them, as i recall but that's fuzzy in my recollection). A population boom around this time is presumed been the impetus for the diaspora. The lack of effect on shellfish fossil sizes brings this presumption into question.

Personally, I have long felt that as we began expanding our minds culturally, there's no reason for a population boom to have "forced" anyone to go explore. It simply supported doing so in a way which was previously not realistic, is what I have always thought. Of course, I am only an interested amateur, not an expert in the field so ...

Maybe they didn't prey on shellfish because they were allergic, didn't like them, or had a religion that worshiped them. I don't prey on the ants that live outside my house but that doesn't mean I don't exist.

YOu wouldn't have an entire population that is allergic. While it's dangerous to assume, of course, one would think that they probably have evidence that humans of this time period were, in fact, preying on shellfish. Dr Curtis Marean has previously published research showing humans were doing so much earlier, ~160K YA, as I recall, though I'm too lazy to dig out the actual cites ... I'm sure they're in the link to him , if you want to dig them up. There's simply no reason to assume humans would stop eating something en masse once they start.

There's plenty of evidence that shellfish was a signficant portion of the human diet (where available).

Exactly. I clarified somewhat. I posted the first version via my phone, which I should know better than to do.

I should also clarify that (to my, albeit limited, knowledge) there is not any particular evidence that shellfish consumption was at such a high intensity that any change in human population would show up as affecting shellfish populations on a macro level. We have evidence that shellfish was more than merely an occasional snack, and that's about all we know.

EDIT: Well, we can surmise that an area with high availability of shellfish would probably result in a human population with a high degree of dependence on that resource, but there are other constraints that might keep utilization of the resource below the level that would drive size-based evolution. And surmising is not really the same as having evidence.

The prequisit for art and cultural explosion should be down to abundance of food and stable climate. With more food available tribes have more free time to take part in leisure activities such as jewellery making.

Maybe they didn't prey on shellfish because they were allergic, didn't like them, or had a religion that worshiped them. I don't prey on the ants that live outside my house but that doesn't mean I don't exist.

YOu wouldn't have an entire population that is allergic. While it's dangerous to assume, of course, one would think that they probably have evidence that humans of this time period were, in fact, preying on shellfish. Dr Curtis Marean has previously published research showing humans were doing so much earlier, ~160K YA, as I recall, though I'm too lazy to dig out the actual cites ... I'm sure they're in the link to him , if you want to dig them up. There's simply no reason to assume humans would stop eating something en masse once they start.

There's plenty of evidence that shellfish was a signficant portion of the human diet (where available).

Exactly. I clarified somewhat. I posted the first version via my phone, which I should know better than to do.

I should also clarify that (to my, albeit limited, knowledge) there is not any particular evidence that shellfish consumption was at such a high intensity that any change in human population would show up as affecting shellfish populations on a macro level. We have evidence that shellfish was more than merely an occasional snack, and that's about all we know.

Back then, yes. More recently, however, it was a significant portion of many people's diet. The Puget Sound's First Peoples have a long history of it, for example, among other foods. We're talking a whole different period, though, and I agree I haven't seen published evidence of it being a primary dietary thing. It would have been a "hey, we're near the beach, let's grab some of those tasty things before swinging back in and looking for antelope tomorrow" kind of thing, I suspect. Still, hunter-gatherers tend to have a regular route for such things, even if it's every other year or something.

It's not evolutionary, it's biological. As shellfish grow, their shells get bigger. When humans prey upon them, we take the biggest (oldest) ones. This leaves fewer of the big ones to become fossils.

Hmmmmm...

I'm going to have to disagree with that vociferously. Its impossible to believe that, over many generations, if humans were selectively culling larger individuals, that it wouldn't drive size-based evolution. These kinds of shellfish are not exposed to size-based selection from other predators at the same rate that they are from humans, so the human pressure would be unique. In fact, one would expect to be able to see the effect of evolutionary pressure from humans even if humans were consuming shellfish at levels too low to detect simple intra-generational population changes (as long as the evolutionary pressure held over many generations). In other words, even if humans were only taking a small percentage of the population (too small for the outcome of a size counts to rise above statistical noise), over many generations the selection pressure would eventually show up in the genetics.

Back then, yes. More recently, however, it was a significant portion of many people's diet. The Puget Sound's First Peoples have a long history of it, for example, among other foods. We're talking a whole different period, though, and I agree I haven't seen published evidence of it being a primary dietary thing. It would have been a "hey, we're near the beach, let's grab some of those tasty things before swinging back in and looking for antelope tomorrow" kind of thing, I suspect. Still, hunter-gatherers tend to have a regular route for such things, even if it's every other year or something.

Yeah, and that's actually the problem, from an archaeological perspective. You go back that far, and they would have mostly been eating shellfish close to where they found them. Not bringing them back up to a cave somewhere for us to find later. It's especially a problem because sea levels have risen, so even if there were semi-permanent campgrounds along the seashore where they ate tons of shellfish over many years, those would be underwater now. (Not just that they are underwater. Even if we knew where to look, much of the evidence would have been destroyed by tides and waves.)

Furthermore, you can only get shellfish consumption up to a certain scale before you need technology we're not sure they had, like baskets to carry large amounts of shellfish around in.

It's not evolutionary, it's biological. As shellfish grow, their shells get bigger. When humans prey upon them, we take the biggest (oldest) ones. This leaves fewer of the big ones to become fossils.

Hmmmmm...

I'm going to have to disagree with that vociferously. Its impossible to believe that, over many generations, if humans were selectively culling larger individuals, that it wouldn't drive size-based evolution. These kinds of shellfish are not exposed to size-based selection from other predators at the same rate that they are from humans, so the human pressure would be unique. In fact, one would expect to be able to see the effect of evolutionary pressure from humans even if humans were consuming shellfish at levels too low to detect simple intra-generational population changes (as long as the evolutionary pressure held over many generations). In other words, even if humans were only taking a small percentage of the population (too small for the outcome of a size counts to rise above statistical noise), over many generations the selection pressure would eventually show up in the genetics.

I'll concede you may be correct but that's not the recollection I have from auditing courses at the UW. It's entirely possible, though, that I am either misremembering or only remembering half the story.

Back then, yes. More recently, however, it was a significant portion of many people's diet. The Puget Sound's First Peoples have a long history of it, for example, among other foods. We're talking a whole different period, though, and I agree I haven't seen published evidence of it being a primary dietary thing. It would have been a "hey, we're near the beach, let's grab some of those tasty things before swinging back in and looking for antelope tomorrow" kind of thing, I suspect. Still, hunter-gatherers tend to have a regular route for such things, even if it's every other year or something.

Yeah, and that's actually the problem, from an archaeological perspective. You go back that far, and they would have mostly been eating shellfish close to where they found them. Not bringing them back up to a cave somewhere for us to find later. It's especially a problem because sea levels have risen, so even if there were semi-permanent campgrounds along the seashore where they ate tons of shellfish over many years, those would be underwater now. (Not just that they are underwater. Even if we knew where to look, much of the evidence would have been destroyed by tides and waves.)

This is quite true. Most of the sites from this era will have been lost completely and, while it's possible a few may be intact below the ocean floor, getting to them is something beyond our current technology. Until we get serious about exploring the alien world just off our shores, that will likely remain the case, too.

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Furthermore, you can only get shellfish consumption up to a certain scale before you need technology we're not sure they had, like baskets to carry large amounts of shellfish around in.

Baskets aren't all they'd have had, though. They probably had hide bags equivalent to baskets but that's also uncertain. As I recall, the effect on the shellfish overall size is created with as little as a dozen folks if sustained for long periods. Since we're talking about very early, pre-village hunter-gatherers, I must agree in general, though that any sustained period of settlement seems unlikely. Still, since we've lost so much of the then-coastal areas, it's very possible that we just don't know about them. If you look at not-quite so ancient peoples and cover up the coastal settlements then you're left with a surprisingly similar story to the ancient African people. Considering these are essentially biologically modern humans, there is no reason to believe things were necessarily all that different behaviorally.

That's one thing that's bugged me for years, in fact. Many First Peoples in the Americas have oral traditions of boats being how their ancestors came to the Americas. Of course, that requires some interpretation but it's pretty common. For decades, the professionals say there's no way because there's no evidence but, in reality, most possible landing sites from that far back are now underwater. While I certainly agree we have no documented proof of it, saying it's impossible is a stretch. We're learning all the time how different history was from what we "knew" it to be for so long.